There are two tracts in the ischioanal region. On the left coronal T2W-images of a small abscess in the left ischioanal fossa, the fistula runs through the levator ani. On the left an example of a complex fistula.
Intersphincteric fistula On the left axial T2W images with and without fat saturation. This fistula breaks through the external sphincter no. On the coronal image the fistula runs caudally towards the skin. This patient was already known to have an intersfincteric fistula, the mucosal defect is at 1 o'clock.
Position of the mucosal opening on axial images using the anal clock. In the tract there is a linear structure with a low signal intensity. Any localizer that properly displays the anal canal can be used.
If there is an extrasphincteric fistula, the lower part is opened. Secondary Iatrogenic hemorrhoideal surgery Inflammatory bowel diseases Crohn's disease more common than colitis ulcerosa Infections viral, fungal or TB Malignancy. The mucosal defect, which is by definition in the rectum, is then surgically closed.
It relaxes during defecation. There is no connection with the external sphincter. On the left a patient with a perianal fistula who has Crohn's disease.